The project will attempt to elucidate the identity, three-dimensional relationships, and chemical properties of the groups which are responsible for the catalysis of conversion of alpha-aminolevulinic acid to porphobilinogen by the enzyme alpha-aminolevulinic acid dehydratase from bovine liver. The tools to be used are probes in the form of isotopically labeled substrates and substrate analogs. Work will include measurement of rates of isotope exchange as a function of pH and substrate analog structure and stereochemistry, measurement of kinetic isotope effects, and affinity labeling to identify active site residues. The enzyme under study is a suspected locus for the effects of lead poisoning. Experiments are proposed to study the interactions of various divalent metal ions, including the native zinc and paramagnetic manganese as well as lead, with the apoenzyme.